Who invented the cardan joint, the wheel, the propeller?

Answer

Such questions are usually very difficult to answer, due to various reasons. Firstly, an invention of a mechanical principle cannot always be assigned to a specific person. The wheel or lever eg. was probably invented by different people, at different times, in different cultures. Second, the answer often depends on a precise definition of the object or instrument. That is e.g. the case for the thermometer. Third, the history of mechanical instruments is poorly documented. It was not until the Renaissance that scientists became seriously concerned with mechanics, and books and treatises were devoted to it. Before that, mechanics was rather a craft whose principles were passed on by craftsmen within master-apprentice relationships.

However, we can answer some of your questions. Many mechanical principles were already known to the ancient Greeks. The most important book on mechanical inventions in the ancient world is The Mechanics of Heron of Alexandria, who lived between 10 and 75 AD. In it he discusses tools for moving heavy objects such as the lever, a wedge, the pulley and the screw. But all these instruments were known for much longer. Heron is said to have gained much of his knowledge from Archimedes (287-212 BC). Many mechanical inventions are attributed to Archimedes such as the principle of moving water in height with a screw. But again, probably such principles were known before.

As for the cardan joint, we can be a little more specific about that. This invention is attributed to Girolamo Cardano (1501-1576). In his book De subtilitate, first published in 1550, he describes various mechanical instruments and principles in an encyclopaedic way. This book was very popular, was reprinted, translated and plagiarized several times. In the first part he describes the principle of the cardan joint, which is therefore named after him. Cardano was a man of genius but lacked the practical experience of engineers. It therefore seems unlikely to me that he was the inventor. Yet he was the first to describe and illustrate the principle. Attached you will find a page from his collected works in which this illustration appears (top right).